What is the Connection Between Epitaxy and Optics?

What does an obscure announcement about beam epitaxy have to do with system-level design?

Plenty, if you’re designing optical network systems (ONS). Such systems continue to find applications in the macro world of computer network and the micro world of Micro-Electro-Mechanical (MEM) chips. The later requires an understanding of microphotonics, which deals with the direction of light on a microscopic scale.

From a material science standpoint, the really tricky part of micro-optics is in the growth of the appropriate epitaxial layers onto silicon wafers. Epitaxy refers to the method of depositing a monocrystalline film (or epitaxial layer) onto a monocrystalline substrate. The key phrase is “depositing a monocrystalline film,” which requires that similar crystalline structures must be grown (or enticed to grow) onto the surface of the silicon wafer. Epitaxy is used in silicon-based manufacturing processes for BJTs and modern CMOS devices, but also GaAs compounds.

Why am I rambling on about epitaxial layers? Aside from the fact that it’s interesting, measuring the purity of such layers was once part of my job. It’s easy to grow oxides on a silicon substrate – just leave the wafer exposed to air for a few hours. But theses are not the expitaxial layers that you want, especially for microphotonic applications. Growing ferroelectric expitaxial layers is needed for such applications, which, for a number of reasons, is a very difficult task.

Now you can understand why I was interested with the recent announcement from the Center for Nanoscale Materials (CNM) at Argonne National Laboratory.

“Complex Oxide Molecular Beam Epitaxy — This technology allows pure complex oxides films to be grown epitaxially; of special interest are films that are ferroelectric, ferromagnetic, or superconducting. Alternating layers can be deposited to allow the observation of novel properties at the boundary or interface.”

From the obscure world of epitaxy to the common world of optical networks, a good system-level designer must know it all. (Eat your heart out, James Burke.)